View original (French)

Check numeric variable

tlep Posted messages 597 Status Member -  
Char Snipeur Posted messages 10112 Registration date   Status Contributor Last intervention   -
Hello,

I'm trying in Perl to check if a variable passed as an argument to a script is numeric.

I successfully tested:
if ($ARGV[2] =~ m/^\d+$/){print "Argument '".$ARGV[2]."' is numeric.\n";}

However, I'm unable to use NOT (to get the opposite):

if (!$ARGV[2] =~ m/^\d+$/){print "Argument '".$ARGV[2]."' is not numeric.\n";}
=> doesn't work
if ($ARGV[2] !=~ m/^\d+$/){print "Argument '".$ARGV[2]."' is not numeric.\n";}
=> doesn't work
if !($ARGV[2] =~ m/^\d+$/){print "Argument '".$ARGV[2]."' is not numeric.\n";}
=> doesn't work

Thank you :-) 
Configuration: Windows XP Firefox 2.0.0.11

7 answers

  1.
    b0rice Posted messages 9 Status Member 1
     
    Hello,

    the negation in a regexp in Perl is: $string !~ m/$re/;

    In your case:

    print 'Argument '.$ARGV[2].' non-numeric' if ($ARGV[2] !~ m/^\d+$/);

    You could also do:

    print "Argument ".$ARGV[2];
    if ( $ARGV[2] =~ m/^\d+$/ ) {
    print " numeric\n";
    }
    else {
    print " alphanumeric\n";
    }

    just simply ;)
    1
  2. Char Snipeur Posted messages 10112 Registration date   Status Contributor Last intervention   1 331
     
    Salut.
    I don't understand why 
    if (!$ARGV[2] =~ m/^\d+$/){print "Argument '".$ARGV[2]."' non numérique.\n";}
    doesn't work. Is it due to operator precedence? Would 
    if (!($ARGV[2] =~ m/^\d+$/)){print "Argument '".$ARGV[2]."' non numérique.\n";}
    work? Otherwise, I'm really confused, the not on a boolean should always work normally.
    --
    Best regards! I used to believe, now I am sure.Jesus Christ
    Char Snipeur
    0
  3. lami20j Posted messages 21506 Registration date   Status Moderator, Security Contributor Last intervention   3 571
     
    Hello,

    here are some tests
    root@debian:~# perl -e 'print "non-numeric\n" if ("aaa" !~ /^\d+$') non-numeric root@debian:~# perl -e 'print "non-numeric\n" if (!("aaa" =~ /^\d+$/))' non-numeric root@debian:~# perl -e 'print "non-numeric\n" unless ("aaa" =~ /^\d+$/)' non-numeric

    --
    106485010510997108
    0
  4. lami20j Posted messages 21506 Registration date   Status Moderator, Security Contributor Last intervention   3 571
     
    ou
     perl -e '"aaa"=~/^\d+$/?"":print "non numérique\n"'

    --
    106485010510997108
    0
  6. lami20j Posted messages 21506 Registration date   Status Moderator, Security Contributor Last intervention   3 571
     
    Another possibility to test non-numeric is with the complemented character class \D that looks for non-numeric characters 
    root@debian:~# perl -e 'print "non-numeric\n" if ("aaa" =~ /^\D+$/)' non-numeric
    this way I don't need to negate
    I simply look for a non-numeric match

    --
    106485010510997108
    0
  7. lami20j Posted messages 21506 Registration date   Status Moderator, Security Contributor Last intervention   3 571
     
    For the info

    !~ it's not quite a negation

    this operator rather means to find the non-match and not to not find the match
    --
    106485010510997108
    0
  8. Char Snipeur Posted messages 10112 Registration date   Status Contributor Last intervention   1 331
     
    Thank you for the clarification.
    --
    Greetings! I used to believe, now I am certain.Jesus Christ
    Char Sniper
    0